This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We propose to study a variety of proteins using synchrotron radiation. These include immunologically important molecules such as catalytic antibodies, anti-HIV antibodies, MHC/TCR complexes, NKG2D-receptor complexes, IL-2/receptor complexes, CD1, and CD3. We will also study the purine biosynthesis enzymes GAR transformylase and ATIC in complex with inhibitors. Finally, we will use the MAD technique to determine the structures for p115, a cell trafficking molecule and for CD14, the main lipopolysaccharide sensor on macrophages.